The present invention relates generally to techniques for decorating and/or labelling articles and more particularly to a novel method for screen printing glass articles and like ceramic ware.
The decorating and/or labelling of commercial articles, such as, and without limitation to, containers, clothing materials, construction materials, artwork and the like, is widespread and well-known. One established technique for decorating and/or labelling articles is screen printing. Screen printing typically uses a porous screen of fine silk, stainless steel or a similarly suitable synthetic fiber that is mounted on a frame. A stencil is produced on the screen, either manually or photomechanically, in which the non-printing areas are protected by the stencil. Printing is screen by applying ink with a paint-like consistency to the screen, and then spreading and forcing the ink through the openings of the screen with a rubber squeegee onto the underlying substrate.
One of the desirable aspects of screen printing is that a thick layer of ink can be deposited onto a desired substrate. Another desirable aspect of screen printing is that a variety of different types of materials can be decorated by screen printing; however, heretofore, the type of material being printed upon has, to some extent, limited the type of screen ink that could be used in printing thereon. For example, ceramic materials, including glass articles, have heretofore required the use of ceramic screen inks. Ceramic screen inks typically include a ceramic material, such as silicon dioxide, which is doped with an inorganic pigment (which is often a derivative of a heavy metal). Such inks typically further include a liquid vehicle, said vehicle often comprising a dispersant and a suitable solvent. If necessary, additives for adjusting the rheology of the ink for screen printing, or other desirable additives, are also included. After a glass or other ceramic article has been screen printed with a ceramic screen ink of the foregoing type, the printed article is typically fired to a very high temperature, causing the liquid vehicle to be burned-off and causing the doped ceramic material to become fused to the article.
Examples of ceramics inks suitable for screen printing are disclosed in the following U.S. patents, all of which are herein incorporated by reference: U.S. Pat. No. 4,043,824, inventor Wagar, issued Aug. 23, 1977; U.S. Pat. No. 4,416,974, inventor Scheve, issued Nov. 22, 1983; U.S. Pat. No. 5,275,649, inventors Linke et al., issued Jan. 4, 1994; and U.S. Pat. No. 5,238,881, inventor Norris, issued Aug. 24, 1993.
One problem with ceramic screen inks is that the colorant/dopant must be an inorganic pigment in order to withstand the high firing temperatures mentioned above. Many inorganic pigments, however, are derivatives of heavy metals (titanium dioxide being a notable exception) and, therefore, pose health and/or environmental risks. Additionally, as can readily be appreciated, the range of different colors afforded by the class of inorganic pigments is limited, due to the constraints of nature, as compared to that afforded by the class of organic colorants.
Still another problem with ceramic screen inks is that one must possess equipment capable of obtaining the very high firing temperatures discussed above in order to cure the ink once printed on the substrate. As can readily be appreciated, the expense of such equipment will, in many instances, preclude all but glass manufacturers from being able to screen print ceramic inks onto glass and the like.
Screen printing is not the only technique presently used to decorate or to label glass articles. One such alternative technique involves the use of heat-transfer labels. One well-known type of heat-transfer label is described in U.S. Pat. No. 3,616,015, inventor Kingston, which issued October, 1971, and which is incorporated herein by reference. In the aforementioned patent, there is disclosed a heat-transfer label comprising a paper sheet or web, a wax release layer affixed to the paper sheet, and an ink design layer printed on the wax release layer. In the heat-transfer labelling process, the label-carrying web is subjected to heat, and the label is pressed onto an article with the ink design layer making direct contact with the article. As the paper sheet is subjected to heat, the wax layer begins to melt so that the paper sheet can be released from the ink design layer, a portion of the wax layer being transferred with the ink design layer and a portion of the wax layer remaining with the paper sheet. After transfer of the design to the article, the paper sheet is immediately removed, leaving the design firmly affixed to the article and the wax transferred therewith exposed to the environment. The wax layer is thus intended to serve two purposes: (1) to provide release of the ink design from the web upon application of heat to the web and (2) to form a protective layer over the transferred ink design. After transfer of the label to the article, the transferred wax release layer is typically subjected to a post-flaming technique which enhances the optical clarity of the wax protective layer (thereby enabling the ink design layer therebeneath to be better observed) and which enhances the protective properties of the transferred wax release.
In some heat-transfer labels, an adhesive layer (e.g., solvent-soluble polyamide, acrylic or polyester) is deposited over the ink design to facilitate adhesion of the label onto a receiving article. An example of a heat-transfer label having an adhesive layer is disclosed in U.S. Pat. No. 4,548,857, inventor Galante, which issued Oct. 22, 1985, and which is incorporated herein by reference. Additionally, in some heat-transfer labels, a protective lacquer layer is interposed between the wax release layer and the ink layer. An example of such a label is disclosed in U.S. Pat. No. 4,426,422, inventor Daniels, which issued Jan. 17, 1984, and which is incorporated herein by reference.
Another type of heat-transfer label (i.e., a wax-less, heat-transfer label) is disclosed in U.S. Pat. No. 4,935,300, inventors Parker et al., which issued Jun. 19, 1990, and which is incorporated herein by reference. In the aforementioned patent, the label, which is said to be particularly well-suited for use on high density polyethylene, polypropylene, polystyrene, polyvinylchloride and polyethylene terephthalate surfaces or containers, comprises a paper carrier web which is overcoated with a layer of polyethylene. A protective lacquer layer comprising a polyester resin and a relatively small amount of a non-drying oil is printed onto the polyethylene layer. An ink design layer comprising a resinous binder base selected from the group consisting of polyvinylchloride, acrylics, polyamides and nitrocellulose is printed onto the protective lacquer layer. A heat-activatable adhesive layer comprising a thermoplastic polyamide adhesive is printed onto the ink design layer.
In general, the ink design layer of the above-described heat-transfer labels is formed by gravure printing onto the protective lacquer layer (or onto whichever layer it is desired to put the ink design layer) a design using an ink formulation comprising an organic resinous binder, a colorant and a vaporizable solvent system. The printed article is then heated, causing the solvent system to evaporate and causing the remaining non-volatile components to be set on the substrate. The resinous binder is typically selected from the group including polyamide, polyester, polyester-vinyl, acrylic, vinyl and acrylic-vinyl resins. The colorant is typically selected from the group including titanium dioxide and organic colorants (e.g., insoluble derivatives of organic dyes).
In those instances in which a heat-transfer label of the type described above is used to decorate a glass container, the glass container is typically pre-treated with a silane adhesion promoter of the type described in U.S. Pat. No. 3,907,974, inventor Smith, which issued Sep. 23, 1975, and which is incorporated herein by reference. The reason for silane-treatment is to make the glass container more receptive to the adhesive layer of the heat-transfer label. Glass containers are typically not receptive to heat-transfer labels because they are usually manufactured with a coating of stearate applied to the outside surface thereof, the stearate-coating impairing adhesion between the heat-transfer label and the glass container. The reason why stearate is typically applied to glass containers is to act as a lubricant to reduce scratching of adjacent glass containers following their manufacture. By silane-treating a stearate-coated glass container, it has been found that one can improve the adhesion between the glass container and a heat-transfer label.